Method of lapping gears



Jan. 29, 1935. R. s. DRUMMOND 1,939,650

' METHOD OF LAPPING GEARS Original Filed June 29, 1931 2 Sheets-Sheet 1INVENTOR ATTORNEYS Jam 29, 1935. s, DRUMMOND I I 1,989,650

METHOD OF LAPPING GEARS Original Filed June 29, 1931 2 Sheets-Sheet 2 vI INVENTOR fiaexf Sirzzmmazr d fb wn mm mMAL ATTORNEY};

Patented Jan. 29, 1935 1,989,650 METHOD OF LAPPING GEARS Robert S.Drummond, Detroit, Mich.

Application June 29, 1931, Serial No.

Renewed July 16, 1934 4 Claims. (Cl. 51-278) The invention relates ofcertain errors which are sometimes developed as an incident to thelapping process. More specifically, the invention relates to the lappingof gears by running the same in mesh with a lap, the axis of which isnon-parallel to the axis of the gear and is not in a common planetherewith. This results in a sliding movement of the gear teeth over theteeth of the lap whch is transverse both to the lines of simultaneouscontact and also transverse to the plane of rotation. As a consequence,the abrading action will be substantially uniform on all high spotsregardless of their location in the surface of the gear teeth. The lapemployed in this method. which may be made of soft metal such as castiron, is originally cut with its involute teeth of the proper helicalangle and of a eontourcorresponding of predetermined radius. Thehowever, is somewhat'in excess of ness which would be proper for amating gear. Consequently the lap is provided with suficient stock inits teeth to compensate for wear and by feeding it inward towards thegear being lapped it may be used until the tooth'thickness is reduced toa predetermined limit.

With the method as above described it has been found that the lappedgears are sometimes noisy even where they are found to be correct incircular pitch and in toot contour. The reason for this was not at firstappreciated but I have disto a base circle tooth thickness, the tooththickcovered that it is due to an error in helical angle of the lappedgear which does not exactly correspond to that of the mating gear. Thereason for this error is that as the lap wears, thecross sectionalcontour of the tooth form is preserved, but as the lap is slightlyreduced in diameter and correspondingly in circumferential length, thiswill slightly alter the helical angle. words, the lead of one end of thetooth in advance of the other end will remain constant and if thecircumferential length is decreased this will alter the helical angle.

Based on this discovery I have modified the method of lapping so as tocompensate for any radial wear in the lap by a corresponding change inthe angle of the axis of the lap with respect to the axis of the gear.If such compensation is made, the lap may be used with satisfactory results through its entire life.

Another important feature of my invention is in the angular arrangementof the axes of rotation of the gear and lap. I have found that the tothe lapping of gearsv .and has for its principal object the eliminationIn other best results are obtained when the, axes are crossed at anangle between 3 and My improved method may be carried out-with difierenttypes of apparatus and may be either manually or automatically.controlled. I shall,

however, describe which the control is nly a simple apparatus in manual.

In the drawings: I Figure 1 is a side elevation of a machine with whichmy method may Figure2 be performed; is a" plan view thereof;

Figure 3 is a sectional elevation showing the lap and the relativearrangement of the same with respect to the gear to be finished.

As shown in detail in Figure 1, A is any suitable machine such as auniversal milling machine of ordinary construction which is providedwith a work table B for supporting a work arbor C on which the gear D tobe finished may be mounted. The table is raised or lowered by suitablemechanism (not shown) controlled by the handle E and the table B ismoved longitudinally or parallel to the arbor C through the operation ofa handle F. There is alsoan adjustment operated by 'the handle G forinward or outward on the bed moving the table Above the table B is thearbor H having the lap I mounted thereon, said arbor being journaled inbearings upon the adjustable slide J relatively movable in a directionparallel to the axis of the arbor. The suitable means such as arbor H isdriven by any the gearing. K.

As shown in detail in Figure-3, the gear D to be lapped is detachablymounted upon the arbor C having a therewith and a clamping nut C inposition.

splined or other driving engagement retains the work Axial movement of Cand C on op- The lap I may be teeth I' thereto the teeth of to be of apre- The helical pitch is,

of course, the same as that of the gear to be lapped but the tooththickness of the lap is greater than that proper for a ating gear of thelapped gear.

the arbor is pre- In the original setting of the machine the lap ismounted upon the arbor H while the gear D to be lapped is mounted uponthe arborC. The table B is then manually adjusted angularly and isaccurately 'set to bring the axis of the arbor H in exactlypredetermined relation to the axis of the arbor C. This relation is suchthat the teeth of the lap will be exactly parallel with the teeth o thegear when the latter are at the exact predetermined helical angle totheaxis of the gear. The table is then vertically adjusted so as toplate a predetermined contact pressure between the teeth of the lap andthe gear. Abrasive material is then spread upon the'surface of thelapand rotary motion is imparted to the machine to cause the gear andlap to run in mesh. This will cause the abrading of the high points onthe teeth of the gear but will also wear the lap so that it is necessaryfrom time to time to further raise the table to renew the desiredpressure contact. This in fact is a very essential part of the process,for I have found that where the gear and lap are permitted to run inmesh without sufiicient contact pressure there will be a. washing actionby the abrasive which will destroy the accuracy of the tooth formed. a

As hasbeen previously described, wear in the lap will cause a change inthe helical angle of the teeth. This is compensated for by acorresponding angular adjustment of the table which may beldeterminedeither by the amount of upward feed of the table since its originalsetting or by testing the gear lapped for correctness of helical angleand then altering the angular setting of the table to correct any error.It is also possible to makean automatic compensation through which thefeeding of the axis of the lap towards the axis of the gear will produceacorresponding angular feeding of the table. However, the specificmechanism, for accomplishing this is not illustrated and therefore willnot be further described.

Certain features of the invention described and illustrated but notclaimed herein are claimed in my co pending applications relating tomethod for finishing gears, Serial No. 604,575, filed April 11, 1932 andSerial No. 626,769, filed July 30, 1932.

What I claim as my inventionis:

1. The method of finishing gears which consists informing a lapping toolhaving teeth conjugate to thegear to be lapped and of such a helicalangle that the axis of the lap will be non-parallel to and have nocommon plane with the axis of the gear when in mesh therewith,relatively adjusting the axes of said gear and lap to an exactlypredetermined angular relation such that the teeth of the lap will beexactly parallel to the teeth of the true gear and will be in pressurecontact therewith, running the gear and lap in meshand simultaneouslyreciprocating one axial- --ly in relation to the other, relativelyadjusting the axes of said gear and lap to compensate for .wear in thelatter and to maintain pressure contact between the teeth thereof andalso relatively adjusting the same angularly to compensate for wear inthe lap so as to maintain the parallelism of the teeth thereof withtheteeth of the true ear.

2. The method of finishing gears which consists in running the gear tobe finished in mesh with alapping tool having conjugate teeth of suchangle to its axis that the latter will be non parallel to and in nocommon plane with the axis of the gear, relatively adjusting the axes ofsaid gear and lap to an exactly predetermined angular relation such thatthe teeth of the lap will be exactly parallel to the teeth of the gearwhen the latter are in the exactly predetermined relation to the axisthereof, and adjusting this angular relation between the axes of thegear and lap to compensate for any wear in the latter so as to maintaina constant angular relation between the teeth of thelap and the axis ofthe gear being lapped.

3. The method of finishing gears which consists in running the gear tobe finished in mesh with a lapping tool having conjugate teeth of suchan angle to its axis that the latter will be nonparallel to and in nocommon plane with the axis of the gear, initially adjusting the axes ofsaid gear and lap to anexactly predetermined angular difference,adjusting said axes towards each other to produce a cramping actionbetween the teeth of the gear and the lap and in subsequently changingthe angular relation of the axis of said gear and lap to compensate forwear in the latter and to maintain a correct helical angle in the gear.

4'. The method'of finishing gears which consists in running the gear tobe finished in mesh with a finishing tool having conjugate teeth of suchan angle to its axis that the latter will be non-parallel to, at anangle less than 30 and in no commonplane with the axis of the gear,initially adjusting the axes of said gear and finish.- ing tool to anexactly predetermined angular difference, adjusting said axes towardseach other to produce a cramping action between the teeth of the gearand the finishing tool and in subsequently changing the angular relationof the axis of said gear and finishing tool to compensate for wear inthe latter and to maintain a correct helical angle in the gear.

ROBERT S. DRU'MMOND.

